The present invention relates to self-sufficient power stations; and more particularly, it relates to a remote power station for converting solar energy to a more useful form of energy, such as electricity or heat.
Systems of the type with which the present invention is concerned have principal application in remote areas where electricity or other utilities are not readily available. In a broader sense, however, persons skilled in the art will readily appreciate that the present invention is more broadly directed to a solar energy conversion system, whether the useful energy is in the form of electricity or heat, and irrespective of its ultimate use. Even though the invention has such broader application, it will be disclosed in the context of a remote source of electrical power such as is used, for example, for cathodic corrosion protection of subterranean metal pipes. Such systems are used in the oil and gas industries, in both drilling and distribution or storage systems.
In cathodic corrosion protection applications, a dc electrical current is continuously generated between a ground bed "sacrificial" electrode (which is the anode or positive terminal) and the metal pipes to be protected (which forms the cathode or negative terminal). The magnitude of the required current is determined by the size of the system being protected and the impedance characteristics of the ground, called the "ground bed" impedance.
Typically, a system of batteries is used to generate the required dc current continuously, and a second source of energy is used to re-charge the batteries. The second source of energy may, for example, by a gasoline or diesel engine and a generator or alternator, a thermoelectric generator, or it may be a solar energy photovoltaic converter. In the past, the most widely used solar energy converters used for remote power stations have employed a number of solar photovoltaic cells mounted to a fixed, planar frame, sometimes referred to as a "flat panel" construction. The flat panel was positioned in a well-known manner to enhance the collection of useful solar energy. It is known that if solar energy falls perpendicularly onto the surface of a solar cell, the energy conversion is at a maximum. The attitude and elevation of a solar flat panel in a fixed position for a given location on earth will provide a known maximum conversion of solar energy over the solar day throughout the year--that is, the number of generated watt hours per day.
However, the number of solar cells required on a fixed flat panel for a usable power station, considering the various positions of the sun throughout the year, is so large that the system has been prohibitably expensive for conventional commercial use. Further, the size of the system required the use of a heavy frame and support structures to provide adequate wind resistance. This further increased the cost of fabricating, installing and maintaining such systems. Exposure to the environment resulted in corrosion, the most frequent cause of system failure.
Thus, a very important aspect of a remote power station is its cost effectiveness--that is, the consideration of initial cost, installation cost, maintenance cost, fuel cost, life expectancy, etc. In a solar energy conversion system, the costs may be divided into three general areas. First, there is the necessary quantity of solar photovoltaic cells required to provide the watt-hours of electrical energy per unit of time (usually the average minimum number of hours of sunchine per day). Secondly, there is the cost of electrical or mechanical parts in the system other than the solar cells, and the production and installation costs. Finally, to be practical, the life expectancy of a solar energy system should be at least 20 years, and therefore, maintenance and repair/replacement costs should be considered as part of the initial design. A common failure of prior systems has been due to physical damage and corrosive effects of exposure to the natural elements of wind, rain, snow, hail, humidity, dust, etc. Prior methods of minimizing the effects of weather have proved either too costly or too ineffective for sustained commercial use.
Various forms of sun-tracking solar conversion systems have been designed which require high motor power; and for the reasons discussed, experienced other cost and reliability disadvantages similar to those associated with the flat panel design.
In the present invention, a number of solar energy converter assemblies are carried by a support frame which is mounted to a gimbal for independent rotation about a horizontal axis and a vertical axis. Separate drive motors are provided for elevation and azimuth control. Solar sensors detect the position of the sun; and control circuitry, responsive to the output signals of the sensors, actuates the drive motors to position the support frame in elevation and azimuth so that the converter assemblies track and face the sun whenever the sun incident energy is greater than a threshold level of about 25% of normal. Because of the ability to track the sun, the present invention has a number of significant advantages as compared to a conventional solar flat panel; among which is the fact that over a given day, it is able to produce more watt-hours of electrical power per unit of time for a given number of solar cells. Hence, the number of solar cells for given electrical requirements will be reduced significantly.
Further, each converter assembly includes a multiangular conical concentrator shell (i.e., formed from at least two frusto-conical elements placed in tandem) designed to collect, concentrate and direct incident solar energy onto the associated cell for conversion.
In this manner, the present invention overcomes many of the economic disadvantages of prior solar flat panel constructions be reducing the number of cells required, and by collecting and concentrating the incident energy onto the available cells. Assuming the same size cells with the same output rating are used, a typical reduction in the number of solar cells is about 85%; that is, only 13 to 15% of the number of solar cells is required for equivalent watt hour output.
The converter assemblies, the support frame and its gimbal mount, and the drive mechanism for the support frame are all located within an enclosed, stationary housing which is transparent to incident solar energy. That is to say, the housing is stationary, and the support frame is free to move within the housing to track the sun. Preferably, the housing is in the form of two flanged hemispherical transparent plastic members sealed and secured together. This feature has several important advantages. First, the support frame and gimbal mount structure for the converter assemblies may be made lighter because it does not have to resist wind forces, thereby simplifying the mechanical support requirements as well as substantially reducing the size and electrical power of the drive mechanisms. Secondly, the sealed enclosure keeps moisture, dust and other weather elements out of contact with the solar cells, the concentrators, the drive mechanisms, and other portions of the system which would otherwise deteriorate if exposed to the elements.
The present invention thus provides a solar energy converstion system which has a cost effectiveness which will permit it to be used commercially as a remote power station. Not only is the initial cost relatively low, but the system is reliable both electrically and mechanically, and the complete environmental protection afforded by a sealed enclosure increases reliability and life and reduces maintenance. The present system provides the solar energy converter assemblies in an electrically and mechanically modular form so that standard "modules", i.e., single self-contained system units or assemblies can be manufactured and connected in series, parallel or series-parallel circuit combinations whenever the user's total power requirements exceed the output capacity of any individual module.
Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing wherein identical reference numerals will refer to like parts in the various views.